fix(workspace): Enter keeps an empty bullet on its level when siblings follow

Outdenting an empty bullet on Enter only happens when no bullet on the
same level follows in the branch; otherwise a new bullet is added below.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/workspace/OutlinerBlock.tsx

@@ -106,6 +106,8 @@ export interface OutlinerBlockProps {
   onPasteMultiLines?: (blockId: string, textBefore: string, textAfter: string, rawLines: string[]) => void;
   /** Number or letter of a numbered-list item ("1.", "b.", "iii.") */
   listMarker?: string;
+  /** Another bullet on the same level follows: Enter in this empty bullet adds a bullet instead of outdenting */
+  siblingFollows?: boolean;
   lockedBy?: string; // someone else is editing this block
   canAppendBelow?: boolean; // the user may edit the note, so Enter in a locked block still adds one below
   onResolveConflict?: (blockId: string, accept: boolean) => void;
@@ -155,6 +157,7 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
   registerTextareaRef,
   onPasteMultiLines,
   listMarker,
+  siblingFollows = false,
   lockedBy,
   canAppendBelow,
   onResolveConflict,
@@ -961,13 +964,13 @@ export const OutlinerBlock: React.FC<OutlinerBlockProps> = ({
 
       const minLevel = levelOffset || 0;
       if (localContent === '') {
-        if (Math.max(0, block.level || 0) > minLevel) {
+        if (Math.max(0, block.level || 0) > minLevel && !siblingFollows) {
           flushDebounce(localContent);
           onIndentBlockRef.current(block.id, -1);
           return;
         }
-        // Enter in an empty numbered item at the top ends the list
-        if (block.type === 'numbered') {
+        // Enter in an empty last numbered item at the top ends the list
+        if (block.type === 'numbered' && !siblingFollows) {
           flushDebounce('', { type: 'text' });
           return;
         }